I. Field
The present invention relates generally to electronic protection circuitry. More, specifically, the present invention relates to an insulated thermal cut-off device.
II. Background Details
Protection circuits are often times utilized in electronic circuits to isolate failed circuits from other circuits. For example, the protection circuit may be utilized to prevent damage from an electrical or thermal fault condition in an electrical circuit, such as in lithium-ion battery packs. Protection circuits may also be utilized to guard against more serious problems, such as a fire caused by a power supply circuit failure.
Some circuit protection devices use a temperature sensing element. Temperature sensing elements can become corroded under high temperature and moisture environments, particularly from moisture with acetate ion and/or acid content. A corroded temperature sensing element may not work properly, causing the circuit protection device to fail. Acetate ions and/or acid content often exist in the thermal cut-off application environment. An electrical insulation tape is often used to isolate the thermal cut-off device and prevent any metal-to-metal contact of the thermal cut-off with other components on a printed circuit board or other substrate. The adhesive of the electrical insulation tape may contain acetate ions and/or acid content, which may be released under a high temperature and high humidity environment. Further, temperature sensing elements comprising materials with better corrosion resistance to acids and other corrosive compounds may have a limited deflection and their thermal expansion characteristics may not be sufficient to allow the manufacture of the desired small devices. Small size thermal cut-off devices are desirable; but to guard against corrosion a designer must sacrifice reliability of the devices for miniaturization.